The present invention relates to a coaxial starter, particularly to a coaxial starter for starting the engine of a vehicle.
FIG. 3 shows a conventional starter 1 for starting the engine of a vehicle. The starter 1 comprises a DC motor 2; an overrunning clutch 4 slidably fitted on an output rotary shaft 3; a planet gear mechanism 5 for transmitting the torque of the armature shaft 2a of the DC motor to the outer member 4a of the overrunning clutch through the output rotary shaft so that the rotation speed of the outer member is lower than that of the armature shaft; and a shift lever 8 which is engaged at one end thereof with the actuation rod of an electromagnetic switch 6 provided at the peripheral portion of the DC motor in order to slide the overrunning clutch on the output rotary shaft and is engaged at the other end thereof with an annular member 7 attached to the overrunning clutch. Since the electromagnetic switch 6 for applying electric power to the DC motor 2 is disposed at the peripheral portion of the motor, the starter 1 is of the two-axis type. For that reason, the layout of the engine in the vehicle is greatly restricted. This is a problem.
In order to solve the problem, a starter having an electromagnetic switch disposed at one end of a DC motor to shape the starter as a simple slender cylinder, was proposed. The armature shaft of the DC motor is hollow. The actuation rod of the electromagnetic switch, which would actuate the shift lever in the starter shown in FIG 3, is moved toward an output rotary shaft through the internal opening of the armature shaft. Since the actuation rod is coaxial to the armature shaft, the starter is called a coaxial starter. Although the coaxial starter is shaped as the simple slender cylinder, the actuation rod extending from the body of the electromagnetic switch into the internal opening of the armature shaft is likely to incline so that the end of the rod moved toward the output rotary shaft does not horizontally push the output rotary shaft at the end thereof through the action of a ball but causes the output rotary shaft to fail to properly slide. This is a problem. Since the electromagnetic switch is disposed behind the DC motor and the actuation rod extends from the body of the switch into the internal opening of the armature shaft through the opening of the wall of the motor, dust or chips generated as a result of the wear of the brushes of the motor are likely to enter into the contact chamber of the switch to cause the contacts thereof to fail to come into proper touch with each other. This is another problem.